In medical and surgical detection equipments, when there is a consumable liquid material that should not be or cannot be transferred between different containers, a liquid level detecting device is usually provided for detecting a certain low level of the liquid. An objective in the design of a detecting device is that the detecting device responds to a small volume or level of remaining or residual liquid, thus the consumption rate of the consumable material can be increased.
In known low liquid level detecting devices, float sensors are generally used for detecting liquid levels. In a float sensor, a float body moves up and down with the liquid surface, thus a magnetic ring enclosed in the float body also moves up and down. When the liquid level in the container is high, the float body is at a high position. On the other hand, when the liquid level in the container falls down to a certain extent, the magnetic ring, falling together with the float body, initiates a magnetic switch by magnetic induction. The magnetic switch sends a signal to a control circuit, which detects out that the liquid level in the container reaches to a low condition.
In such a float sensor, under the limitation of the above magnetic induction principle, the float sensor is generally bulky. Meanwhile, since the weight of the float body is high, the lowest liquid level necessary to cause the lowering float body initiating the magnetic switch is relatively high. In this condition, during detection, when the sensor responds to the float body moving close to the bottom portion of the container, the level of the remaining liquid in the container is still relatively high, which results in that it cannot effectively reflect whether the liquid level really reaches to the bottom portion of the container.